1. Field of the Invention
The present invention is directed generally to a voltage tester for optically displaying graduated voltage levels applied to test tips, or probes. The voltage tester includes a circuit arrangement of electrical components including a first series circuit composed of a first PTC-resistor, two light-emitting diodes connected antiparallel to one another and at least one drop resistor that is balanced so that one or both light-emitting diodes light up when a voltage exceeding a particular level of, for example, 4.5 volts and, in particular, 6 volts is applied to the test tips.
The invention is directed particularly to a voltage tester wherein individual electrical components having power leads are accommodated in the overall circuit arrangement of a device composed of two handles that are connected to one another by a connecting cable. The device also includes test tips or probes as well as openings in the handles through which the optical display components are observed.
The present invention is also directed to a method for manufacturing a voltage tester.
2. DESCRIPTION OF THE RELATED ART
German Patent 20 60 884 discloses a test means for indicating the polarity or phase relation of electrical potentials relative to a prescribed reference potential. The reference potential, in particular, periodically changes between two potentials in switching devices having ambivalent switching variables in the form of a reference potential whose value differs on the basis of a phase difference of 180.degree.. The test means uses a series circuit composed of two light-emitting diodes antiparallel to one another as well as a preceding, current-limiting resistor. The two light-emitting diodes are arranged protected in at least one opening of a grip-shaped housing which also contains the current-limiting resistor and which carries a metal tip at its face end. The grip-shaped housing includes an oblong opening which is covered by a light transmissive material and behind which is arranged for protection the two light-emitting diodes following one another with their light-emitting sides directed outwardly. At one end, the grip-shaped housing carries a part of an electrical plug connection for accepting a corresponding other part which includes a test line.
An improvement in the above-described test means is disclosed in U.S. Pat. No. 4,210,862 by which a test can also be carried out for current conduction through a line by using an additional circuit with a battery. All components of the disclosed device are accommodated in a handle that is provided with a test tip and which is connected via a cable to a second handle that also has a test tip.
The light emitting diode pairs in these are connected antiparallel to one another. In other words, the diodes are connected parallel to one another with their respective polarities reversed so that the anode lead of one diode is connected to the cathode lead of the second diode. The antiparallel connection of the two light emitting diodes results in only the light emitting diode which is switched to the conducting mode lighting up when a DC voltage is applied to the test tip, while the second light emitting diode is in a non-conductive, inhibiting mode. The polarity of the DC voltage connected to the appertaining test tips determines which of the two light emitting diodes lights up. When an alternating voltage is applied to the two test tips, logically, both light emitting diodes light up.
European Patent Document B 0 011 711, corresponding to U.S. Pat. No. 4,301,407, discloses a test means for graduated display of a test voltage which includes two handles provided with contact tips that are connected by a cable. One of the handles contains a display unit which has a series circuit of non-linear luminance elements, as well as a voltage divider composed of a plurality of series connected resistors, the series circuit being charged by a test voltage. The base of a transistor is connected to each of the taps of the voltage divider formed by the junction of the resistors. The emitters of these transistors are connected to one lead, or post, of one of the luminance elements, and the collector of the transistor is connected to the collectors of the remaining transistors as well as to a lead or pole of a power supply whose other pole is connected to other lead of the luminance elements at the end of the series circuit. FIG. 4 of the European and corresponding U.S. patent, as well as the appertaining description, discloses a circuit containing further light emitting diodes as well as glow lamps, in addition to an antiparallel circuit of two light emitting diodes that are connected in series with a PTC-resistor.
The test devices described above exhibit a number of considerable advantages in practical applications. Such advantages include, among other things, that the voltage to be tested is displayed in graduated fashion divided into a greater number of voltage ranges, for example, including voltage ranges between at 6 volts, 12 volts, 24 volts, 50 volts, 110 volts, 220 volts, 380 volts, and 600 volts. Nonetheless, the outlay or expense both in view of the necessary electrical components as well as in view of the manufacture of both the motherboard carrying the components and printed interconnects as well as the equipping thereof with the electrical components is extremely high.
European patent document B 0 068 501, corresponding to U.S. Pat. No. 4,527,118, discloses a test means of the type described above that is again improved. In addition to the previous, graduated display of the voltage to be identified, the test means also provides for the possibility of testing an electrical line for current conduction, for which purpose a battery is contained in the circuit. Additional possibilities include carrying out a function test of individual components and identifying voltage sources having high internal resistances, i.e., voltage sources that are not mains voltage sources, by preconnecting a high impedance drop resistor and a connectable load resistor circuit composed of a plurality of PTC-resistors and normal resistors. One of the two handles of the test means that are connected to one another by a cable accommodate at least one high impedance drop resistance and the load resistor circuit.
Due to their advantages, a great number of the test devices described above are in use.
However, it has also been shown that less of a graduation of the individual display ranges for the voltages to be identified is adequate for many applications. For example, the display of voltage ranges beginning with 4.5 volts, beginning with 50 volts, and beginning with 110 volts are advantageous. The two first voltage ranges are still relatively non-hazardous to the individual operating the voltage tester, although voltages above 110 volts are extremely dangerous, particularly when voltage levels of 220 or even 380 voltage are exceeded. It is, therefore, adequate to provide an unambiguous optical display that contrasts with the other voltage ranges for this last voltage range.
German published application 31 48 382 discloses an electrical means, and particularly an electrical tool, with plugable components and a connection plate for plugging and connecting the components to one another and/or to the power supply. The connecting plate comprises a network of conductive metal strips or wires that are embedded in plastic. Electrical components such as, for example, electrical resistors, light emitting diodes, Zener diodes or PTC-resistors are applied to this connecting plate.